Cataract is the most common cause of blindness in the world today. Surgery is generally very effective in restoring sight; however, a common complication is the development of posterior capsule opacification. This is caused by aberrant growth and differentiation of lens cells that remain in the capsular bag after surgery. Our approach to circumvent this problem is to identify the conditions required for normal growth and differentiation of residual lens cells and apply this new information to promote regeneration of normal lens structure and function. Our previous NEI-funded studies showed that members of the FGF growth factor family could induce fiber differentiation in vitro and subsequent studies by our group and others have now provided compelling evidence that fiber differentiation in vivo depends on FGF signaling. This knowledge is fundamental to devising strategies for lens regeneration after cataract surgery. However, if we are to successfully regenerate transparent lenses with normal focusing abilities, in addition to being able to initiate and promote fiber differentiation, we need to be able to recapitulate the coordinated cell behavior that is required to generate the exquisite three-dimensional organization of fibers (and epithelial cells) that is the central feature of normal lens morphogenesis. In our current NEI-funded project we have identified Wnt/Frizzled signaling through the planar cell polarity (Wnt-Fz/PCP) pathway as critical for promoting the precise alignment/orientation of fibers. We have also shown that epithelial cells provide a polarizing cue that aligns/orients elongating fibers. To exploit these novel findings this renewal application aims to elucidate the mechanism(s) whereby activation of Wnt-Fz/PCP signaling translates into polarized fiber cell behavior and establishes the global alignment/orientation of fibers that is critical for normal lens morphogenesis. In section 1 of the project we will use FGF to induce fiber differentiation in our well- characterized epithelial explant system to identify the mechanism whereby components of the Wnt-Fz/PCP signaling pathway organize the lens cell cytoskeleton and promote coordinated alignment/orientation. In section 2, using epithelial explants and complementary transgenic approaches we will both promote and inhibit Wnt bioavailability and/or Wnt signaling to determine if epithelial-derived Wnt ligand provides a directional cue that draws fibers to poles This project will provide vital new information about mechanisms and molecules that are required to promote the regeneration of lens structure and function and in so doing will address key objectives identified within the Lens and Cataract Program of the NEI.